How to Find an Engine's Top Dead Center


It is necessary to find the top dead center of a car engine if the distributor has to be removed for some reason. All cars come from the factory with a timing mark on the crankshaft pulley, but sometimes the mark gets broken off. Here's how to find top dead center if there is no timing mark.

  • Make an indicator using a jar of light oil, a old spark plug and a clear plastic tubing. Put the plastic tubing on the end of the spark plug after you break up the spark plug to make it air tight.

  • Take all the spark plugs out of the engine. Turn the engine with your thumb in the number one spark plug hole until you feel pressure on your thumb. The top of this stroke is the top dead center, or the compression stroke. You can use the starter to turn the engine over, but if you feel more comfortable with the battery cable unhooked, you can use a wrench on the alternator to turn it. You can also use a wrench on the crankshaft pulley.

  • Put the spark plug with the plastic tubing in the number one spark plug hole. Place the other end of the tubing into the jar of light oil. As you keep turning the motor, bubbles will be blown into the oil until the piston reaches the top. When the piston starts back down, the oil will be sucked into the tube. Stop and mark the engine body and the crank pulley. Also mark the tube where the oil stopped.

  • Turn the engine backwards and the oil will go back into the jar. Keep turning the motor until the oil is sucked back into the tube. Stop at the mark and the pulley should line up with the first mark you made. Make another mark on the crank pulley and the midpoint between the marks should be top dead center.

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